At a minimum, any new 35mm format mount would be backwards compatible with EF. For example, with the direction DSLRs have been going, I could envision the eventual need for fancy video targeted lenses that may need additional contacts for continuous AF/iris/aperture or who knows what else. But as long as the same image circle is cast, and the film plane is at the same distance, why come up with a whole new mount?

Nikon is still using the same mount they have always had, but at the time, Canon needed to alter the FD mount to make way for auto focusing. It is doubtful that the mount would change again. The EOS/EF system is flexible and should be able to handle a lot more future changes.

Let's consider what would "kill" EF mount. The only thing I can think of is EVIL, and even then that's a bit of a stretch. I'm not talking short term here, but suppose in the distant future we have an EVIL camera with AF system that is as good as DSLR phase AF in every way. That would be enough to obsolete crop sensor DSLRs, and only leave FF serving a niche position (unless Canon goes FF EVIL!), and who knows by then "affordable" medium format might be squeezing that space too.

The post above on video is interesting but I'm not familiar enough with it to guess any possible impact there. Videographers seem to be doing well enough with current kit. What lens functionality additions would increase value for video use? Consider what might be done in body as opposed to lens too.

I could envision the eventual need for fancy video targeted lenses that may need additional contacts for continuous AF/iris/aperture or who knows what else.

This is exactly the type of speculation I was looking for... The developments in high definition video recording make one wonder how much longer Canon will be able to utilize the same mount!

Couldn't they simply add a couple of contacts to new lenses and new bodies, while maintaining backward compatibility with current lenses. There's plenty of room around the mount ring. For example, the lenses compatible with the 1.4x and 2x extenders have 3 extra contacts for the TC (there are no contacts for them on the bodies).

I could envision the eventual need for fancy video targeted lenses that may need additional contacts for continuous AF/iris/aperture or who knows what else.

This is exactly the type of speculation I was looking for... The developments in high definition video recording make one wonder how much longer Canon will be able to utilize the same mount!

Couldn't they simply add a couple of contacts to new lenses and new bodies, while maintaining backward compatibility with current lenses. There's plenty of room around the mount ring. For example, the lenses compatible with the 1.4x and 2x extenders have 3 extra contacts for the TC (there are no contacts for them on the bodies).

What concerns me the most with adding anything to the current technology, is the marginal increase in size and weight (which I believe is one of the key limitations of current photographic equipment).

Alas, what I would like to see (a full-frame system the size of today's "point and shoot" toys - and I use that terminology loosely), is probably many decades from fruition.

I could envision the eventual need for fancy video targeted lenses that may need additional contacts for continuous AF/iris/aperture or who knows what else. But as long as the same image circle is cast, and the film plane is at the same distance, why come up with a whole new mount?

You could use a kind of auto negotiation, if both camera and body support it you switch to a new protocol. Or simply increase the rate of updates to the framerate. Its an SPI connection after all. Canon could get respond times in the single digit ms range, if they want. I'd reckon the motors are the weaker links.

The main reason for a new mount would be a shorter flange focal distance. Nothing a simple adapter without image quality degrading optics couldn't handle.